About

Dept. Electromagnetic Neurophysiology

INTRODUCTION

The Department of Electromagnetic Neurophysiology, founded in May 2010, is a research facility of the Smart Ageing International Research Center (SAIRC). Our mission is to investigate brain physiology through electromagnetic measurement and stimulation, to develop the electromagnetic tools for research and medicine, and to promote clinical applications of electromagnetic neurophysiology. Here we describe four representative methods of electromagnetic neurophysiology: electroencephalography (EEG), magnetoencephalography (MEG), electrical brain stimulation, and magnetic brain stimulation.

EEG

Brain neuronal currents can be measured electrically by EEG. EEG provides lots of information about normal brain function and abnormal activity related to disease. Scalp EEG is a common noninvasive technique, providing routine examinations for various types of brain diseases. However, the spatial resolution of scalp EEG is limited because of serious distortion effects caused by inhomogeneous head conductivity. For more accurate measurement of brain signals, intracranial electrodes can be used to perform corticography, brain surface EEG or electrocorticography (ECoG), and deep brain EEG or depth EEG. Intracranial EEG is indicated only for patients with specific diseases such as medically intractable epilepsy or brain tumors. However, intracranial EEG also provides unique opportunities to investigate human neurophysiology. Intracranial EEG can be measured intraoperatively, or extraoperatively using chronically implanted electrodes. Many opportunities to use intracranial EEG are available since Dr. Nobukazu Nakasato, Professor and Chairman of the Department of Electromagnetic Neurophysiology, heads the Department of Epileptology, Tohoku University Hospital.

MEG

Brain neuronal currents can be magnetically measured by MEG. However, the MEG signal is extremely weak in the order of fT (femto tesla = 10-15 tesla), so measurement requires a specially designed magnetically shielded room and high sensitivity magnetic sensors called a superconducting quantum interference device (SQUID). Recent developments of low temperature technology have enabled construction of helmet-shaped MEG systems with multichannel SQUID sensor arrays. Despite the large-scale equipment, MEG provides higher spatial resolution than scalp EEG since MEG suffers far lower distortion effects caused by inhomogeneous head conductivity. MEG research in Tohoku University started in 1987, and many articles have been published on brain mapping of somatosensory, auditory, gustatory, visual, and language functions. We have also accelerated the diagnostic application of MEG for epilepsy and ischemic brain diseases. Now we will embark new era of MEG, as Dr. Ryuta Kawashima, Director of SAIRC, introduced a new MEG system in March 2010 and Dr. Nobukazu Nakasato was appointed as the Chairman, Department of Electromagnetic Neurophysiology in May 2010.

ELECTRICAL BRAIN STIMULATION

The brain can be electrically stimulated directly during surgery (intraoperative cortical stimulation), or using chronically implanted intracranial electrodes (extraoperative cortical stimulation). Intracranial stimulation is exclusively limited to preoperative brain mapping for patients with specific diseases such as medically intractable epilepsy or malignant brain tumors. However, modern neuroscience has greatly developed with clinical experience, illustrated by the famous human brain mapping pioneered by Wilder Penfield and his colleagues.

MAGNETIC BRAIN STIMULATION

The brain can be stimulated magnetically by transcranial magnetic stimulation (TMS) using electrical coils on the head to generate a brief magnetic field which penetrates the cerebral cortex. TMS is usually coupled with electromyography response detection to assess cortical excitability based on the threshold required to induce motor evoked potentials. TMS can be used for brain mapping, and neuromodulation therapy for treating depression or other neurological diseases.

HISTORY AND FUTURE

Dr. Koichi Motokawa, Ex-Chair of the Department of Physiology, and Ex-President of Tohoku University, started the pioneering research work of EEG here in Sendai before World War II. We are also proud of our pioneering work of MEG since 1987. Our new department aims to expand the previous concept of “electrophysiology” into “electromagnetophysiology.” Our facility welcomes highly motivated young researchers and physicians.